1. Field of the Invention
The present invention relates generally to a system for protecting individuals engaged in activity around operating machinery and, more particularly, to a personnel warning and machinery disabling system for alerting and protecting individuals straying into a hazardous zone in a mine and/or straying too close to operating machinery.
2. Background Description
Personnel unknowingly entering into areas in close proximity to operating machinery may place themselves in danger and be injured or killed. Consequently, ways of preventing such injuries are constantly being investigated. In coal mining, a well known major safety concern is that of personnel becoming permanently disabled or killed by machinery or by powered haulage. Between 1992 and 1997, 24 fatalities were associated with continuous mining machines. At least some of these accidents occurred because mining machine operators and their assistants become preoccupied with operating the coal mining equipment and unwittingly place themselves in potentially hazardous locations, i.e., within the danger zone of the operating machinery.
In addition, the operator must perform a variety of tasks with the machine, each of which may raise a potential hazard or increase visual requirements such that the operator does not always have a good visual sense of the machine""s location or whether someone is within the zone of danger. It has been found that a large portion of the time, operators still place themselves unknowingly within the hazard zone, even while the machinery is operating.
One way that mine safety has been improved is by using radio remote-control to place operators away from the hazards of operating machinery. These remote-controlled machines allow the operators greater mobility so that the operator can see potentially critical worksite areas that would otherwise not be visible to an onboard machine operator. However, the remote operators are still vulnerable, and not always aware of their position. So, they may still occasionally stray into the hazard zone near an operating machine.
Furthermore, after turning off equipment or machinery with the remote control, e.g., to service the machine, the operator may intentionally enter the danger zone. As long as the machine is disabled, the operator is safe. When the operator is servicing the machine, however, someone else, unaware of the operator""s location, might use the remote control to reactivate the machine, thus placing the servicing operator in danger.
So, especially in the close quarters of a mine entry, it is important to know, as precisely as possible, when the operator or other personnel are within a safe distance of operating machinery or when they have entered the danger zone. To that end, U.S. Pat. No. 5,939,986 entitled xe2x80x9cMobile Machine Hazardous Working Zone Warning Systemxe2x80x9d to Schiffbauer et al., issued Aug. 17, 1999, teaches a warning system for mobile working machinery that includes loop antennas that are distributed about mining machinery to define a warning zone. The direction of the radiation from each loop is perpendicular to that loop. The shape of the zone is determined by the shape of each loop antenna field decreases with one over the cube of the distance from the loop. A personnel warning device and receiver is worn by a protected individual and includes a single ferrite loop antenna that receives the signal as a person enters the field.
While the system taught in Schiffbauer et al. provides some warning to the wearer, it does not provide positional accuracy because both the loop radiation and the receiver antenna are directional. At any distance from the loop, signal strength is maximum when the receiver antenna is parallel to the loop and is minimum when the receiver antenna is perpendicular to the loop. So, signal strength varies depending upon the direction of the single receiver antenna to the loop antenna, at any given distance from the loop. Thus, it is difficult to determine whether the signal strength is due to antenna alignment or distance from the loop.
Accordingly, there is a need for a safety system to make a machine operator aware of the danger zone, to warn the operator, and selectively disable the machine when the operator is in the zone of danger or when others enter the zone of danger. More particularly, a safety system is needed that provides better precision in terms of when an operator is in a danger zone, substantially irrespective of the relative orientation between the transmitter and receiver antennas.
It is therefore a purpose of the invention to reduce the hazard to operators of machinery.
It is another purpose of the invention to warn machine operators when they or other personnel enter the danger zone of operating machinery.
It is yet another purpose of the invention to stop operating machinery when the operator and/or others unintentionally enter the danger zone.
It is yet another purpose of the invention to disable operating machinery when persons enter the danger zone of the operating machinery.
It is yet another purpose of the invention to improve the sensitivity and/or accuracy of personnel safety equipment around hazardous machinery.
The present invention is a hazardous area warning system with a non-directional magnetic field based proximity receiver for warning personnel of an attendant hazard. The receiver which is worn by an operator (or other personnel) and provides feedback (e.g., warning lights, sound, and/or vibrations) to the wearer as to proximity to a danger zone defined by a magnetic field generated by a transmitter thereto. The receiver minimizes the directional effects inherent in the relative orientation between antennas of the receiver and transmitter of prior systems, providing a more accurate feedback to the operator in hazardous condition areas. In a preferred form, the receiver includes a x-axis receiver with an antenna directed in a x direction, a y-axis receiver with an antenna directed in a y direction and a z-axis receiver with an antenna directed in a z direction. The antennas may be a wire loop wrapped around a ferrite core. The output from each of the three receivers are combined in an adder. The combined result from the adder is representative of the distance between the receiver and a warning transmitter antenna. A comparator determines whether the received signal indicates an attendant hazard, i.e., the receiver is too close to the warning transmitter. Warning devices, such as, for example, visual, audio, and/or vibrational device may be incorporated into the receiver to alert the wearer of the receiver that he/she has entered a hazardous area as indicated by activation level of the received signal. An encoder encodes the signal indication and a transmitter transmits the encoded signal. A data link receiver located, for example at a potentially hazardous machine, receives the encoded signal from the proximity receiver. The data link receiver decodes the encoded signal and activates a safety indicator light or other warning device, preferably mounted on or near the operating machine, in response to the decoded information. Preferably, a green light indicates normal operation, a yellow light indicates a caution or potentially hazardous condition, and a red light indicates danger. The data link receiver may shutdown and/or disable the machinery in a caution or dangerous condition. Advantageously, the receiver of the system of the present invention is omni-directional and provides much better positional accuracy for warning personnel when entering potentially hazardous areas. Further, the system of the present invention can shut down and disable dangerous equipment when personnel are in the machinery""s danger zone.